In this vehicular air-conditioning device, an inner wall surface along a width direction of an air-conditioning casing is provided with guide portions each extending in a vertical direction. The guide portions are recessed on the outside in the width direction, forming recesses with respect to the inner wall surface. When an evaporator is inserted from above the air-conditioning casing and assembled inside, second seal portions of side plates disposed on side surfaces of the evaporator are respectively inserted into the guide portions, whereby the evaporator is guided along the vertical direction. The guide portions further include an entry portion disposed at an upper end portion of a first guide wall and expanding in a direction away from a second guide wall. Thus, the evaporator can be inserted into the air-conditioning casing from above in a preferable manner.